Apparatus for identifying a second of two successive pulses of the same polarity in a pulse train of positive and negative pulses for generation of synchronization pulses for an internal combustion engine

ABSTRACT

Synchronization pulses for an internal combustion engine are generated by identifying the second of two consecutive pulses of the same polarity in a pulse train of positive going and negative going pulses. An evaluation pulse sequence is generated which switches from a low level to a high level in response to a positive going pulse and from the high level to a low level in response to a negative going pulse. A synchronization pulse is generated in response to a differentiated pulse derived from the pulse train when the level of the evaluation pulse sequence indicates that a switching pulse of said same polarity as that of the differentiated pulse has just occurred.

BACKGROUND OF THE INVENTION

This invention relates to apparatus for electronically generatingsynchronization pulses for an internal combustion engine.

In an internal combustion engine having a fuel injection system or someother operation which must be synchronized with engine rotation, it isnecessary to generate a timing signal identifying the rotationalposition of the engine for controlling the operation. The timing signalis usually in the form of periodically generated synchronization pulseswhich occur in relation to the top dead center position of a specifiedengine cylinder.

In many known systems the synchronization pulses are derived from avoltage signal produced by a detector or sensor which indicates theengine speed and crankshaft position.

For example the synchronization pulses may be derived from the voltagesignal produced by a crankshaft transmitter. This voltage signaltypically consists of a series of alternate positive and negative pulsesgenerated as the crankshaft rotates, with an additional pulse beinggenerated at a certain reference position, e.g.; the top dead centerposition of the first cylinder.

In one known system the crankshaft transmitter is placed adjacent aslotted or toothed disc which rotates with the crankshaft. Thetransmitter produces alternate positive and negative pulses as the teethpass it. A magnet is provided at the reference position and thus anextra pulse is generated each time the magnet passes the sensor.

The voltage signal from the crankshaft transmitter thus consists of aseries of alternate negative and positive pulses with two consecutivepulses of the same sense at regular intervals.

It is possible to generate, from the crankshaft transmitter voltage, apulse sequence which switches from a first level to a second level inresponse to a negative going pulse and from the second level to thefirst level in response to a positive going pulse. This pulse sequenceis hereinafter referred to as the negative/positive evaluation signal.This has been achieved using an integrated circuit together with anumber of external components and has been used in many hybridelectronic ignition devices. Suitable circuitry for generating such apulse sequence is described in detail in DE-OS 3208262.

It is desirable to generate the synchronization pulses from thecrankshaft transmitter voltage using as little as possible additionalcircuitry.

In hybrid devices only a limited space can be made available forimplementing the circuit. This means that all functions additionallyneeded must be incorporated into existing or new integrated components.It is obviously advantageous, to incorporate additional functions intoexisting components wherever possible.

It has been proposed to utilise the circuitry for generating thenegative/positive evaluation signal for generating the synchronizationpulses. However, the previous proposals have required modifications tothe integrated circuit.

SUMMARY OF THE INVENTION

The present invention provides apparatus for identifying the second oftwo consecutive pulses of the same polarity in a pulse train of positivegoing and negative going pulses, the apparatus comprising means forgenerating an evaluation pulse sequence which switches from a firstlevel to a second level in response to a positive going pulse and fromthe second level to the first level in response to a negative goingpulse means for differentiating the positive and negative going pulses;and means for generating a synchronization pulse in response todifferentiated pulse which coincides with a level of the evaluationpulse sequence that has been switched by a pulse of the same polarity inthe pulse train as that of said differentiated pulse.

Preferably the synchronization pulse generation means is enabled anddisabled in response to changes of level in the evaluation pulsesequence. Thus, the synchronization pulse generation means is onlyenabled when the evaluation pulse sequence is at said level indicatingthat a second consecutive pulse of same polarity has occurred.

The present invention may thus be very simply accommodated in a knowncircuit for generating a negative/positive evaluation signal. Theevaluation signal is simply used to control a further pulse generatorfor generating synchronization pulses. The two pulse generators may beincorporated in the same integrated circuit.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention will now be described by way of exampleonly and with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of a circuit embodying the present invention and

FIG. 2 shows the waveforms of voltages at different places in thecircuit of FIG. 1 on parallel time axes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The crankshaft transmitter voltage is applied to the input GE1 of anintegrated circuit 10 along line 11 via resistor R1. The waveform of thevoltage at point A in the circuit is shown in FIG. 2. The circuitrycomprising input terminals GE1, F1 output terminal, GA1 of theintegrated circuit and the external components R1, R2, R3, R4; C1, C2,C3 and D1 produces the negative/positive evaluation signal at point B.An output waveform is produced at B which switches from a first level toa second level when the voltage at A drops below a first threshold leveland switches from the second level back to the first level when thevoltage at A rises above a second threshold level. In the illustratedexample as seen in FIG. 1, the integrated circuit includes two constantcurrent generators CG₁ connected between GE1 and a Schmitt triggerswhose output is connected to GA1. The input F1 is a control input forthe constant current generators CG₁.

The generation of the synchronization pulses is implemented by resistorsR5, R6, R7, a capacitor C4 and input terminals GE2, F2 and outputterminals GA2 of the integrated circuit. As with GE1, GA1 and F1, twoother constant current generators CG₂ are connected between GE2 and aSchmitt triggers' whose output is connected to GA2. F2 is the controlinput for the other constant current generators. The output terminal GA1of the integrated circuit 10, delivering the negative/positiveevaluation signal to point B, is fed back to the input terminal F2 alonga line 12 via resistor R5. Capacitor C4 operates to differentiate thecrankshaft transmitter voltage applied to the input terminal GE1. Thedifferentiated signal from the capacitor is applied along a line 13 toinput the terminal GE2 via the junction of resistors R6 and R7 whichform a potential divider.

Referring to FIG. 2, the crankshaft transmitter voltage A consists of aseries of alternate positive and negative pulses with two consecutivenegative pulses at regular intervals. The negative/positive evaluationsignal at point B switches from high potential to low potential when thecrankshaft transmitter voltage at point A drops below a certain negativepotential and from low potential to high potential when the crankshafttransmitter voltage rises above a certain positive potential. Thisswitching is brought about by the Schmitt triggers. Thus, the second oftwo consecutive negative pulses from the transmitter has no effect onthe negative/positive evaluation signal because at this stage theSchmitt trigger is already off.

The output voltage of the capacitor C4 at point C in the circuit isshown in FIG. 2. The synchronization signal from the output terminal GA2at point D in the circuit is also shown in FIG. 2. Referring to theregion marked X in the capacitor output waveform at C, the voltage at Dfrom output terminal GA2 switches from high to low potential when thecapacitor voltage at C drops below a first predetermined level and fromlow to high potential when the capacitor voltage rises above a secondpredetermined level. The circuit of FIG. 1 distinguishes the second oftwo consecutive negative pulses from the first one by actuating theoutput terminal GA2 only after the evaluation signal at B after GA1 hasgone to low potential. Referring to the region marked Y in the capacitoroutput waveform at C it can be seen that by the time the evaluationsignal at B switches to low potential the capacitor voltage at C hasalready risen above the first predetermined level and so thesynchronization signal at D does not switch to low potential.

The detailed operation of the circuit is as follows: when output GA1(point B) is at high, the input F2 drives constant current sources CG₂at the input GE2 into conduction to such an extent that the current ofthe differentiated pulse from GE1 via C4 (point C) cannot cause thecurrent sources at GE2 to switch. If output GA1 is at low potential, theconstant current sources CG₂ are almost cut off by F2. Thisswitching-off process can be extended by control input an additionalcapacitor C5 shown in dotted lines, if required. The operation point forGE2 is then determined by the voltage at the junction between resistorsR6 and R7. If C4 is correctly dimensioned, GA2 switches to low with thenext negative edge at GE1 i.e. the next negative pulse from thetransmitter as shown in FIG. 2.

If the falling edges of negative pulses and rising edge with positiveare steeper than their associated rising and falling edges respectively,it is possible to switch GA2 only at the steeper edges by appropriatedimensioning of C4, R6, R7.

Under certain circumstances it may be necessary to insert a furtherdiode D2, shown in FIG. 1, between lines 12 and 13 for a definedswitching to high of GA2 with the positive pulse.

The circuit described above has a number of advantages over previouslyproposed arrangements. Firstly, the previous proposals all requireadditional hardware expenditure, for example flip flops and analogueamplifiers.

Because space in hybrid devices is limited this necessitates developmentof new integrated circuits or reworking of existing integrated circuits.The present invention saves time and cost on reworking and developmentsince existing functions of the integrated circuit can be utilised.

The circuit is particularly versatile since the differing edgesteepnesses can be utilised by appropriate dimensioning of thecomponents.

I claim:
 1. An apparatus for identifying the second of two consecutivepulses of the same polarity in a pulse train (A) of positive andnegative pulses, comprising means for generating an evaluation pulsesequence connected to receive said pulse train, said evaluation pulsesequence switching from a first level to a second level when a positivepulse in said pulse train is received by said means for generating theevaluation pulse sequence, and from the second level to the first levelwhen a negative pulse in said pulse train is received by said means forgenerating the evaluation pulse sequence; means for differentiating thepositive and negative pulses of the pulse train (A) connected to receivesaid pulse train (A) so as to produce a differentiated pulse when apositive or a negative pulse is received by said means fordifferentiating; and means for generating a synchronization pulseconnected to said means for differentiating to receive saiddifferentiated pulses therefrom and connected to said means forgenerating said evaluation pulse sequence to receive said evaluationpulse sequence therefrom, so that one of the synchronization pulses isgenerated when a differentiated pulse coincides with a level of theevaluation pulse sequence which had been switched by a pulse in thepulse train having the same polarity as that of said differentiatedpulse.
 2. Apparatus as claimed in claim 1 in which the synchronizationpulse generation means is enabled and disabled in response to changes oflevel in the evaluation pulse sequence.
 3. Apparatus as claimed in claim1 in which the train of pulses is conveyed to the synchronization pulsegeneration means via the differentiating means (C4).
 4. Apparatus asclaimed in claim 3 in which the differentiating means comprise acapacitor.
 5. Apparatus as claimed in claim 4 in which thesynchronization pulse generation means is arranged when enabled toswitch from a first level to a second level when the capacitor outputvoltage falls below a first predetermined value and to switch from thesecond level to the first when the capacitor output voltage rises abovea second predetermined level.
 6. Apparatus as claimed in claim 1 inwhich the means for generating a first pulse sequence and the means forgenerating the synchronization pulses are incorporated in an integratedcircuit.
 7. Apparatus as claimed in claim 1 wherein the means forgenerating the first pulse sequence and the means for generating thesynchronization pulses each comprise two constant current generatorsconnected to a threshold switching device.
 8. Apparatus as claimed inclaim 7 in which the evaluation pulse sequence is used to control thetwo constant current generators of the means for generating thesynchronization pulses.
 9. Apparatus as claimed in claim 7 in which theconstant current generators and the threshold switching devices areincorporated in an integrated circuit.
 10. Apparatus as claimed in claim7, in which each of the threshold switching devices comprises a Schmitttrigger.